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PubMedDate not supplied

Forward masking is dependent on inner hair cell activity.

The goal of this study was to test the hypothesis that the inner hair cell complex (inner hair cell and dendritic contacts) is solely responsible for generating the slope of the forward masking curve. To test this hypothesis two experiments were performed. The first was to measure forward masking from the Bronx waltzing mouse, a mutant possessing an inner hair cell defect. The Bronx waltzing mouse demonstrated an approximately 60-dB auditory brainstem response (ABR) threshold shift compared to CBA/CBA mice at 8 and 12 kHz. The slope of the forward masking curve was significantly reduced compared to the control group, particularly at the early delay times between 0 and 4 ms. The second model employed kainic acid to affect the dendrites beneath the inner hair cell. After the intracochlear infusion of kainic acid, there was an approximately 47-dB ABR threshold shift at 4 and 8 kHz compared to pre-infusion thresholds. The slope of the forward masking curve from the kainic-acid group was significantly reduced compared to the artificial-perilymph group. Primarily the early delay times were affected by kainic acid (0-4 ms). Morphological analysis showed that there was extensive swelling of the afferent nerve radial dendrites under the inner hair cells. The results from the present study, as well as the preceding article, suggest that the analysis of the slope of the forward masking curve may be used for the detection of inner hair cell or radial dendrite damage, independent of outer hair cell damage. The present finding could provide a useful means of employing a clinical test for determining the function of the inner hair cell complex using a non-invasive measure of auditory function.

Animals↗
PubMedDate not supplied

Differences in forward masking after a temporary and a permanent noise-induced hearing loss.

The forward masking curve of the auditory brainstem response (ABR) at selected frequencies together with the quantification of hair cell loss through the analysis of cochlear surface morphology was studied in guinea pigs before and after acoustic trauma resulting in either a temporary or a permanent threshold shift. In the presence of a noise-induced temporary threshold shift, the slope of the forward masking curve was not significantly different from the pre-exposure curve. In contrast, during the acute phase of the permanent threshold shift, the slope of the forward masking curve was significantly reduced compared to the pre-exposure value. After a recovery period of 2 weeks, the slope of the forward masking curve from the permanently damaged group returned to nearly normal values despite a persisting ABR threshold shift and significant loss of outer hair cells. The potential for analyzing the slope of the forward masking curve in order to distinguish between the acute phase of a permanent threshold shift and a temporary threshold shift is discussed.

Animals↗
PubMed2002

Suppressive and facilitatory spatial interactions in foveal vision: foveal crowding is simple contrast masking.

Spatial interactions are a critical and ubiquitous feature of spatial vision. These interactions may be inhibitory (reducing sensitivity as occurs in crowding) or facilitatory (enhancing sensitivity). In this work, we had four goals. 1. To test the hypothesis that foveal crowding depends on target size by measuring the extent of crowding for novel targets that were limited in their spatial frequency content. We used a large range of target sizes and spatial frequencies. 2. To assess whether the critical spatial frequency model (Hess, Dakin, & Kapoor, 2000) provides a general model for foveal crowding. To test this model, we measured crowding for a direction-identification task that did not require judging the orientation of the gap. 3. To test the hypothesis that foveal crowding is simply contrast masking by remote flanks we measured and compared crowding in a direction-identification experiment with masking by remote flanks in a detection experiment. In each of the experiments, our targets and flanks were composed of Gabor features, thus allowing us to control the feature contrast, spatial frequency, and orientation. 4. To assess the relationship between suppressive and facilitatory spatial interactions in foveal vision. Our results show that (1) foveal crowding is proportional to feature size over the more than 50-fold range of target sizes that we examined. Over this large range, foveal crowding is scale invariant. Our results also show it is the size of the envelope (SD) rather than the carrier (SF) that determines the extent of crowding in the fovea. 2. Crowding that occurs in the direction-identification task is quite similar to crowding where orientation information is available. Thus we conclude that the critical spatial frequency model does not provide a general explanation for foveal crowding. 3. Threshold elevation for crowding is similar to threshold elevation for masking as predicted by our test-pedestal model. Thus we conclude that foveal crowding is simple contrast masking. 4. Based on our comparison of threshold changes in crowding and masking, we conclude that in foveal vision, the suppressive spatial interactions due to nearby flanks are similar in the two tasks. However, the facilitatory interactions are quite different. In the crowding task, we find very little evidence for facilitation by flankers, whereas in the detection task, we find strong facilitation. We suggest that facilitation of detection by remote flanks may be, at least in part, a consequence of uncertainty reduction.

Contrast Sensitivity↗
PubMed2005

Event-related gamma activity in schizophrenia patients during a visual backward-masking task.

OBJECTIVE: Schizophrenia patients experience deficits in many aspects of cognition and perception. Abnormalities in gamma activity may underlie some of these deficits, including rapid processing of visual stimuli. This study examined event-related gamma range activity during a visual backward-masking task in schizophrenia patients and normal comparison subjects. METHOD: Event-related gamma activity was recorded in 15 normal comparison subjects and 32 schizophrenia patients. Participants had event-related gamma activity recorded while viewing 60 unmasked visual targets and 240 trials of visual backward masking. Effects of group, accuracy (correct versus incorrect), stimulus-onset asynchrony, and regional activity (left versus right hemisphere, anterior versus posterior regions) were assessed. RESULTS: Schizophrenia patients had significantly reduced gamma activity in relation to comparison subjects during the backward-masking task. Normal comparison subjects showed significantly greater gamma activity in the right hemisphere, whereas schizophrenia patients did not show this pattern of lateralization. For the unmasked target, there was no group effect and no significant interactions in gamma-band responses. CONCLUSIONS: These results extend previous findings of abnormal gamma range activity in schizophrenia patients. Patients showed overall less gamma activity and failed to show lateralization of activity to the right hemisphere during masking, but they showed comparable levels of gamma activity to unmasked stimuli. Schizophrenia patients' poorer performance during a masking task may be partly influenced by this abnormal level and the distribution of gamma activity.

Adult↗
PubMed1980

Effect of practice on visual backward masking.

Five experiments studied practice effects for 4, 7, 11 subjects on visual backward masking using a signal-detection procedure under various conditions. Exp. I determined the minimum perceptible critical stimulus duration (CSD) for criterion identification of a target stimulus, the letter T or A. In Exp. II, the stimulus was presented at the critical stimulus duration (CSD) followed by a pattern mask at intervals of 20 to 120 msec. for 15 separate sessions. In Exp. III (N = 4) the mask followed the CSD in intervals of 2-msec. increments until subjects reached criterion accuracy. Exps. IV and V (Ns = 4, 7) provided partial replications of Exps. II and III. Naive subjects were used, and the stimulus duration was constant for all subjects. When masking functions were obtained at a threshold, considerable variability was found and subjects improve slowly or not at all over sessions. With a fixed supra-threshold stimulus, all subjects improve with practice. The inportance of these findings is discussed as they relate to common (and largely untested) assumptions made in the backward masking and perception literature.

Adult↗
PubMed2004

An audit of the Single Use Portex Laryngeal Mask.

We performed an audit of the insertion of the Single Use Portex Laryngeal Mask in 400 patients. Insertion was successful at first attempt in 335 out of 400 patients (83.8%). However in 15 patients (3.8%), the Portex laryngeal mask could not be placed despite repeated attempts. In 12 of these 15 patients (80%), a standard Laryngeal Mask Airway (LMA) was successfully placed. After the completion of the audit, 22 out of 29 anaesthetists (75.9%), who had inserted > or = 5 Portex laryngeal masks, considered it inferior to the standard LMA. It would appear to us that the Portex laryngeal mask might need some design modifications to be a real alternative to the standard LMA.

Adult↗
PubMed2006

Protein contamination of the Laryngeal Mask Airway and its relationship to re-use.

The Laryngeal Mask Airway is a reusable device for maintaining the patency of a patient's airway during general anaesthesia. The device can be reused after it has been cleaned and sterilized. Protein contamination of medical instruments is a concern and has been found to occur despite standard sterilization techniques. The reason for the concern relates to the possibility of the transmission of prions and the risk of developing a neurodegenerative disorder such as Creutzveldt-Jacob disease. The purpose of this study was to quantify the amount of protein contamination that occurs, and to relate this to the number of times the Laryngeal Mask Airway has been used. Fifty previously used Classic Laryngeal Masks were collected after routine sterilization and packaging. The devices were immersed in protein detecting stain and then visual inspection performed to assess the degree and distribution of the staining. The researcher was blinded to the number of times the Laryngeal Mask Airway had been used. Linear regression analysis of the degrees of staining of the airway revealed that protein contamination occurs after the first use of the device and this increases with each subsequent use. This finding highlights the concern that the currently used cleaning and sterilization methods do not prevent the accumulation of proteinaceous material on Laryngeal Mask Airways. Consideration should be given to the search for more efficient cleaning and sterilization techniques or the use of disposable devices.

Equipment Contamination↗
PubMed1992

Alveolar oxygenation and mouth-to-mask ventilation: effects of oxygen insufflation.

The effect on alveolar oxygen fraction (FAO2) of insufflating oxygen under a mask (or through an inflow nipple provided in the mask) during simulated mouth-to-mask ventilation was investigated using a lung model. A variety of commercially produced masks were evaluated. Two patterns of artificial ventilation were applied: 1. 500 ml tidal volume at 20 breaths per minute, and 2. 900 ml tidal volume at 12 breaths per minute. The ventilating gas mixture was oxygen 16% in nitrous oxide, and oxygen was insufflated at flow rates of 2, 4, 6, 8, 10, 12 or 14 litres per minute. The rate of rise of FAO2 and the equilibrium FAO2 attained were greatest at high oxygen inflow rates. The relationship between oxygen flow and FAO2 was not linear however, and an oxygen flow rate of 10 l/min was adequate to generate FAO2's around 50% with either ventilatory pattern. The equilibrium FAO2 achieved was greater with smaller tidal volumes and with larger mask deadspace. We also found that several breaths were required for equilibration of FAO2 during each trial, supporting recommendations that several breaths should be given on commencement of artificial ventilation during cardiopulmonary resuscitation.

Equipment Design↗
PubMed1994

The incendiary characteristics of the laryngeal and reinforced laryngeal mask airway to CO2 laser strike--a comparison with two polyvinyl chloride tracheal tubes.

The incendiary characteristics of the laryngeal and reinforced laryngeal mask airway to the CO2 laser have been compared with two polyvinyl chloride tracheal tubes. Three different power densities (2.35, 4.7 and 9.8 x 10(3) watt/cm2) were used, with either oxygen or a 30% oxygen/70% nitrous oxide mixture flowing down the tube. The laryngeal mask airway (and reinforced model) was shown to be more resistant than the polyvinyl chloride tracheal tubes. The laryngeal mask tube could not be ignited at a power density of 2.25 x 10(3) watt/cm2 after five minutes, although penetration occurred in 20-30 seconds. A layer of silica ash built up at the impact site and protected the underlying tube. The laryngeal mask airway cuff was penetrated at 3 to 5 seconds. At this power density the polyvinyl chloride tube ignited in 2 to 8 seconds and the cuff was penetrated in 0.1 seconds. At the highest power density the tubes of all airways ignited within 0.2 seconds. The possibilities for improving the incendiary characteristics of the laryngeal mask airway are discussed.

Carbon Dioxide↗
PubMed1997

Laryngeal mask insertion following inhalational induction in children: a comparison between halothane and sevoflurane.

The aim of this study was to compare laryngeal mask insertion conditions following inhalational induction with either halothane or sevoflurane. Fifty-eight healthy children scheduled for dental extraction were randomly assigned to receive nitrous oxide 66% in oxygen and 3.0 MAC of either halothane or sevoflurane introduced in a stepwise fashion. The laryngeal masks were inserted when an adequate depth of anaesthesia was attained and the reactions and time to insertion noted. Inhalational induction was smooth in both halothane and sevoflurane groups. Induction time and time to laryngeal mask insertion were significantly faster with sevoflurane. The conditions for laryngeal mask insertion were generally good with 86.2% and 89.2% in the halothane and sevoflurane groups respectively having had no reactions to insertion. The complications to laryngeal mask insertion encountered were mild. The emergence time from the anaesthetic was found to be shorter for sevoflurane but the difference was not statistically significant.

Anesthesia, Dental↗
PubMed2004

Nasal versus full face mask for noninvasive ventilation in chronic respiratory failure.

This study was undertaken to determine the efficacy of nasal mask (NM) versus full face mask (FFM) for the delivery of noninvasive ventilation (NIV) in subjects with nocturnal hypoventilation. A total of 16 patients (11 males) were enrolled, all with nocturnal hypoventilation currently treated at home with NIV via pressure preset devices. Subjects underwent full polysomnography on three occasions; on the first night current therapy on NM was reviewed, followed by two experimental studies in randomised order using either NM or FFM. NIV settings and oxygen flow rate were the same under both conditions. Notably, 14 of the 16 subjects required the use of a chinstrap to minimise oral leak. Apnoea-hypopnoea indices were within normal limits under both conditions (1.7 +/- 3.4 NM versus 1.6 +/- 2.4 h FFM). The type of interface did not significantly affect gas exchange during sleep (minimum average arterial oxyhaemoglobin saturation total sleep time 93.4 +/- 2.1 NM versus 92.8 +/- 2.5% FFM, Delta transcutaneous carbon dioxide nonrapid eye movement sleep to rapid eye movement sleep (0.58 +/- 0.36 NM versus 0.50 +/- 0.40 kPa FFM). Sleep efficiency was significantly reduced on the FFM (78 +/- 9 NM versus 70 +/- 14% FFM), although arousal indices were comparable under both conditions (15.6 +/- 9.8 NM versus 15.8 +/- 8.8 h FFM). Full face masks appear to be as effective as nasal masks in the delivery of noninvasive ventilation to patients with nocturnal hypoventilation. However, a chinstrap was required to reduce oral leak in the majority of subjects using the nasal mask.

Adult↗
PubMed1998

Mask intermittent positive pressure ventilation in chronic hypercapnic respiratory failure due to chronic obstructive pulmonary disease.

Noninvasive ventilation in chronic obstructive pulmonary disease (COPD) has been shown to improve arterial blood gases but its long-term role has not been established. We retrospectively studied 26 consecutive patients with hypercapnic ventilatory failure due to COPD in whom oxygen therapy caused worsening hypercapnia (defined as a rise in the daytime arterial carbon dioxide tension (Pa,CO2) to >8.0 kPa or nocturnal transcutaneous carbon dioxide tension (Ptc,CO2) to >9 kPa). All were treated with mask ventilation (15 with nasal and 11 face masks) at night and during daytime naps. Additional oxygen therapy was required in 15 patients. The mean annualized death rate was 10.8% with a 1 and 3 yr survival of 92 and 68%, respectively. After 1 yr the median daytime Pa,CO2 had fallen by 1.35 kPa and the arterial oxygen tension (Pa,O2) had risen by 2.4 kPa. In subjects not using additional oxygen the median overnight Sa,O2 rose by 12% and the Ptc,CO2 fell by 2.8 kPa after 1 yr. The haematocrit was significantly less than pretreatment at 6 months and 1 yr. Quality of life in the domain of role limitation by physical health (measured using the SF-36 questionnaire) improved significantly at 6 months. Survival in this selected group with clinically stable airflow obstruction unable to tolerate oxygen therapy and treated with noninvasive mask ventilation is better than historical controls and is comparable to those able to tolerate oxygen therapy. Poor survival was associated with a low forced expiratory volume in one second, a low body mass index and a high nocturnal transcutaneous carbon dioxide tension. No difference in survival was found between those treated with mask intermittent positive pressure ventilation alone or with mask intermittent positive pressure and supplementary oxygen therapy.

Adult↗
PubMed1994

Oxygen leakage around the laryngeal mask airway during laser treatment of port-wine stains in children.

The flash-lamp pumped pulsed dye laser is the current treatment of choice for cutaneous port-wine stains. In our practice, most children with these lesions are treated under general anesthesia. At energy levels used clinically, it is possible to ignite hair in the presence of supplemental oxygen; we are aware of four cases in which either the eyebrows or eyelashes were ignited during the administration of general anesthesia via a face mask. The laryngeal mask airway (LMA) recently has become widely available and this device might decrease the risk of fire during treatment of these lesions. We therefore designed this study to examine the extent of oxygen leakage under the mask during clinical cases, and to compare this with the leakage present with the LMA. A total of 20 patients aged 4 mo to 16 yr were studied on 26 separate occasions. During spontaneous ventilation, high concentrations of oxygen leaked around the mask in every case (mean 63% +/- 16%), but in only one case was a concentration more than 21% detected around the LMA (P < 0.001). During controlled ventilation with the LMA, oxygen leaked around the mask in 19% of cases. Use of the LMA markedly decreases the incidence of potential oxygen leakage into the laser field, and is recommended for use, with preservation of spontaneous ventilation, during these cases. We suggest measuring oxygen concentrations at the mouth for laser treatment of facial port-wine stains to confirm that the larynx has been isolated.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Noninvasive face mask ventilation in patients with acute respiratory failure.

Noninvasive face mask ventilation has been used successfully in patients with paralytic respiratory failure. This study evaluated whether noninvasive face mask ventilation can be used for patients with acute respiratory failure due to intrinsic lung disease. Six patients with hypercapnia and four with hypoxemic acute respiratory failure met clinical and objective criteria for mechanical ventilation, which was delivered with pressure control and pressure support via a tightly strapped, clear face mask. No patient terminated the study because of inability to deliver adequate ventilation or to improve oxygen exchange; three eventually required endotracheal intubation. The mask was generally well tolerated. All patients had a nasogastric tube placed on suction, and none vomited or aspirated. The mean duration of treatment was 33 h (range, 3 to 88). The physiologic response was considered similar to that which would have been achieved with conventionally delivered ventilation. Noninvasive face mask ventilation may have a role in managing respiratory failure.

Adult↗
PubMed1995

Effects of frequency on free-field masking.

As three-dimensional auditory displays become more prevalent, there will be an increasing need to understand the interactions that can be expected among spatially separated sounds. A two-alternative, forced-choice, adaptive staircase procedure was used to measure the detectability of a 165-ms click-train signal masked by a continuous Gaussian noise, as a function of the spatial separation between the signal and the masker in the free field. Horizontal separations within the horizontal plane and vertical separations within the median plane were examined for low-, mid-, and high-frequency stimuli. Masking was reduced by as much as 18 dB when the signal and masker were separated horizontally. Sizable reductions in masking (6-9 dB) were also observed for vertical separations. The largest reductions in masking were observed for the high-frequency stimuli. The data are compared with the results of headphone-based studies of binaural masking. Implications for the design of auditory displays are considered.

Adult↗
PubMedDate not supplied

[Continuous positive airway pressure (CPAP) with face mask to treat acute respiratory failure].

OBJECTIVE: To evaluate the efficacy of continuous positive airway pressure (CPAP) administered by face mask in patients with acute respiratory failure with indication of mechanical ventilation. MATERIALS AND METHOD: Eleven patients (mean age 41.3 years) in acute respiratory failure were admitted in the Respiratory Unit--Hospital São Paulo--Escola Paulista de Medicina. At the admission pH, PaO2, PaCO2, respiratory rate (f), arterial pressure and heart rate were measured. The measurements were repeated with administration of oxygen with a high flow face mask at ambient airway pressure and then with 5 cm H2O of CPAP by face mask. RESULTS: The use of CPAP by face mask significantly improved the arterial blood oxygenation and decreased the respiratory rate (p < 0.05). CONCLUSION: These data allow the conclusion that CPAP administered by face mask improves gas exchange and decreases respiratory rate in patients with acute respiratory failure and may reduce the need for invasive mechanical ventilation.

Acute Disease↗
PubMed1993

Two-year follow up on the protective value of dust masks against farmer's lung disease.

Some advocate moving away from the farm environment for farmers affected with farmer's lung disease (FLD), but most affected farmers still live on farms. In this study, we evaluated the practicality of dust masks and their effectiveness in prevention of FLD. The dust masks we chose were practically used and no new severe episodes of FLD developed in 20 of 21 farmers with FLD using the masks during a 2-year period. When the farmers took off the dust masks in a farming environmental provocation test, statistically significant reductions in FVC (mean 3.43 to 3.351, p < 0.01), DLco (mean 19.6 to 18.2 ml/torr/min, p < 0.01), and DL/VA (mean 5.1 to 4.8 (x10(-3)) 1/torr/min, p < 0.01) were observed several hours after exposure. These findings suggest that the dust masks were used practically during routine dairy farming and were effective in protection against FLD.

Adult↗
PubMed1985

Interhemispheric visual masking.

Backward masking functions were evaluated in a paradigm in which target and masking stimuli were presented to opposite cerebral hemispheres using separate peripheral pathways. Backward masking occurred dichoptically when the target and mask were projected to opposite hemispheres. These findings indicated that some effective masking mechanisms are mediated by interhemispheric interactions independent of retinal phenomena.

Adult↗